Interferometric Measurement of Stochastic Path-length Fluctuations in an Interferometer aimed at Optical Fourier-transform Spectroscopy

Optical interferometers are the workhorse components of many different forms of Fourier-transform spectroscopy, including Fourier-transform infrared spectroscopy (FTIR), two-pulse correlation spectroscopy, and multidimensional coherent spectroscopy (MDCS). In order for these elements to function properly in devices, it is vital that the random fluctuations in the associated interferometric optical path lengths be either actively eliminated or passively measured and subtracted out from the final data so that signals of interest can be separated from noise. In this research project, we report a dual-phase measurement of optical path length noise in a Mach-Zehnder interferometer incorporating home-built photodetectors and field-programmable gate array (FPGA)-based analog-to-digital signal converters. We use the setup to monitor the effect of ambient laboratory temperature fluctuations on interferometer dimensions, extracting an optical table’s thermal expansion coefficient in the process.